Over the past several decades, both the business and science communities have employed client-server architectures to sufficiently meet their application processing requirements. As the applications become more and more complex, the need for more powerful servers to run the applications has increased. For example, more powerful servers enable more accurate and more rapid scientific calculations and simulations. In addition, it is often desirable to run the more complex applications, or at least the complex parts of applications, on a powerful server, while running the simpler applications on a client computer. For example, internet search companies run complex search filters on remote servers, while the results are displayed on the users' PCs using simpler display programs.
Over the last ten years, and especially in the last five years, clusters of large numbers of simple servers have emerged as a leading solution for high powered servers. Sometimes these clusters comprise hundreds or even thousands of servers. Many of the servers and switches in these clusters are connected by cables, predominantly copper cables. For example, each blade server in the datacenter may have three different cables attached to it—one for management purposes (typically Gigabit Ethernet cable), one for storage, and one for CPU-to-CPU interconnects (increasingly Infiniband cable). This copper cabling is extremely heavy and has a large cross section, thus consuming a vast amount of space in the small datacenters. The copper cabling is also mechanically temperamental. Because of its heavy weight, copper cabling places stress on the connectors. Therefore, if somebody accidentally bumps into a cable, it can stop working. Additionally, the copper cabling has a long bend radius, thus reducing flexibility.
Furthermore, copper cable simply cannot perform effectively over long distances at high data rates. As data rates increase, the span of copper cable over which an electrical signal may propagate while incurring tolerable degradation is decreasing. Currently, at 20 Gbps, electrical signals can only travel about 10 meters over copper cable before the signal degrades beyond tolerable limits.